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BUILD THE

ALARM
AUTODIALER

By Dan Gravatt

Anyone who owns a
house and is away at
work or on a vacation
will at some point
wonder "What's going on
at home?" Not necessarily
with the kids, but with
the house itself. Even
newer homes can have
problems with heating,
cooling, plumbing, or
electrical systems which
are easier and less
expensive to fix when
discovered sooner rather than later. This
device will detect and report several
common failures with household systems,
so you can deal with them while they are
still easy to fix. It's inexpensive ($60 or less,
depending on your parts collection), easy
to build, and doesn't require any contracts
with monitoring services.

■ FIGURE 1. The alarm autodialer.

Note temperature sensor on side of case.

PROJECT GOALS

Of course, there are off-the-shelf systems and
services out there for automated reporting from smoke
alarms and security systems, but I wasn't interested in
simply duplicating those capabilities (though this project
can be used to monitor those types of alarms). I wanted
to monitor what I think of as the "Big 4" failure types:

36 August 2012

extended power failure; air conditioner failure; furnace
failure; and flooding. I wanted to be notified by phone of
each different type of problem as it occurred. Finally, I
wanted to be notified if the problems corrected
themselves (electrical power being restored, for example)
before I cut my vacation short or called my neighbor to
check on my house.

This project meets those goals without needing a lot
of direct connections to the systems being monitored.
Power failure is detected with an optocoupler interface
to the AC mains (through a wall wart type power supply)
and a battery backup power supply which keeps the
system running and reporting additional problems as they
occur. Air conditioner and furnace operation is
monitored with a DS1621 I2C temperature sensor and
user-defined high and low temperature limits. Flooding is
detected with simple pairs of electrodes which can be
located to check for burst pipes (in the winter), failed
sump pumps (in the rainy season), or both. Three
additional inputs are available for monitoring other
systems as needed.